#include <iostream>
#include <queue>
#include <cstring>

using namespace std;

const int N = 1e6 + 10;
typedef pair<int, int> PII;
int n, m, idx;
int h[N], e[N], ne[N], w[N];
int dist[N];
bool st[N];

void add(int a, int b, int c)
{
    e[idx] = b;
    w[idx] = c;
    ne[idx] = h[a];
    h[a] = idx++;
}

int dijkstra()
{
    memset(dist, 0x3f, sizeof(dist));
    dist[1] = 0;
    priority_queue<PII, vector<PII>, greater<PII>> heap;
    heap.push({0, 1});
    while (heap.size())
    {
        auto t = heap.top();
        heap.pop();
        int var = t.second;
        if (st[var])
        {
            continue;
        }
        st[var] = true;
        for (int i = h[var]; i != -1; i = ne[i])
        {
            int j = e[i];
            if (dist[j] > dist[var] + w[i])
            {
                dist[j] = dist[var] + w[i];
                heap.push({dist[j], j});
            }
        }
    }
    if (dist[n] == 0x3f3f3f3f)
    {
        return -1;
    }
    return dist[n];
}

int main()
{
    memset(h, -1, sizeof(h));
    cin >> n >> m;
    while (m--)
    {
        int a, b, c;
        scanf("%d %d %d", &a, &b, &c);
        add(a, b, c);
    }

    printf("%d", dijkstra());
    return 0;
}
